The alarm sounded because of a sensor error, said Wang at a press conference.

"We were quite nervous when the astronaut in the re-entry module reported the fire alarm. However, we became quite relaxed after knowing the fire alarm was from the orbital module because it was opened to the vacuum of outer space and no air was there to ignite the flame," Wang told reporters.

Taikonaut Zhai Zhigang floated out of Shenzhou-7 at around 4:40 p.m. (Beijing Time) Saturday and stayed in space for about 20 minutes, accomplishing China's first attempt on an extravehicular activity (EVA).

Through the live broadcast of the mission, the wheezing sound of Zhai was heard when he managed to open the hatch strenuously.

Wang admitted it took a little bit longer than people had expected for Zhai to open the hatch, as it was much more difficult for him to complete the move in space than on the ground despite of thorough preparations beforehand.

"Although the astronaut has undergone tremendous training and tests on the ground, the vacuum and zero-gravity conditions can not be completely simulated during the training," he said.

"The environmental difference between outer space and ground makes our maiden spacewalk more difficult, which is within our expectation," he said. "But it increased our understanding about outer space, and prompted us to do more research." he added.

Zhai's spacewalk marked a remarkable progress in the country's ambitious space programme that will eventually lead to the establishment of a permanent space station.

Originally published by Xinhua news agency, Beijing, in English 1421 27 Sep 08.